A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One example of the fuel cell is a Proton Exchange Membrane (PEM) fuel cell. The PEM fuel cell includes a membrane-electrode-assembly (MEA) that generally has a thin, solid polymer membrane-electrolyte having an anode and a cathode with a catalyst on opposite faces of the membrane-electrolyte. The MEA is generally disposed between a pair of porous conductive materials, also known as gas diffusion media, which distribute gaseous reactants, e.g. hydrogen and oxygen/air, to the anode and cathode layers. The hydrogen reactant is introduced at the anode where it reacts electrochemically in the presence of the catalyst to produce electrons and protons. The electrons are conducted from the anode to the cathode through an electrical circuit disposed therebetween. Simultaneously, the protons pass through the electrolyte to the cathode where an oxidant, such as oxygen or air, reacts electrochemically in the presence of the electrolyte and catalyst to produce oxygen anions. The oxygen anions react with the protons to form water as a reaction product.
The MEA of the PEM fuel cell is sandwiched between a pair of electrically-conductive bipolar plates which serve as current collectors for the anode and cathode layers. The bipolar plates include a plurality of lands and flow channels for distributing the gaseous reactants to the anodes and cathodes of the fuel cell. The bipolar plates serve as an electrical conductor between adjacent fuel cells and are further provided with a plurality of internal coolant channels adapted to exchange heat with the fuel cell when a coolant flows therethrough. The typical bipolar plate is a joined assembly constructed from two separate unipolar plates. Each unipolar plate has an exterior surface having flow channels for the gaseous reactants and an interior surface with the coolant channels. In order to conduct electrical current between the anodes and cathodes of adjacent fuel cells in the fuel cell stack, the paired unipolar plates forming each bipolar plate assembly are mechanically and electrically joined.
A variety of bipolar plate assemblies and methods for preparing bipolar plate assemblies are known in the art. For example, it is reported by Neutzler in U.S. Pat. No. 5,776,624, incorporated herein by referenced in its entirety, that a bipolar plate including corrosion-resistant metal sheets may be brazed together so as to provide a passage between the sheets through which a dielectric coolant flows. Further, U.S. Pat. No. 6,887,610 to Abd Elhamid, et al., incorporated herein by reference in its entirety, discloses a bipolar plate assembly without welding or brazing that includes an electrically conductive layer deposited over the coolant channels and lands and a fluid seal disposed between the inside facing surface about a perimeter of the coolant channels. Also, U.S. Pat. No. 6,942,941 to Blunk et al., incorporated herein by reference in its entirety, recites a bipolar plate having a first and second surface that are coated with an electrically conductive primer coating and joined to one another by an electrically conductive adhesive. Schlag in U.S. Pat. No. 7,009,136, incorporated herein by reference in its entirety, describes a method of fabrication adapted to weld bipolar plates together using a partial vacuum that holds paired unipolar plates together during the welding process.
There is a continuing need for a bipolar plate assembly having an efficient and robust internal architecture that provides an optimized electrical contact between the plates of the assembly. A method for rapidly preparing the bipolar plate assembly applicable to conventional flowfield designs is also desired.